Dev: use build product flavors for app store release (#1205)

## Description
Instead of applying a code patch, this PR uses build time [product
flavors](https://developer.android.com/build/build-variants#product-flavors)
to define the existing default and an app store variant. This is more
robust than maintaining a patch file and making sure it is applied
before building.

The app store variant applies the same code changes (removing install
permission, requiring leanback, & setting `UpdateChecker.ACTIVE`), but
via manifest placeholders/merging and `BuildConfig` entries.

There are no user facing changes.

### Related issues
None

### Testing
Built the variants and verified manifest changes via aapt

## Screenshots
N/A

## AI or LLM usage
None

.github/workflows/pr.yml

@@ -39,19 +39,6 @@ jobs:
       - name: Build app
         id: buildapp
         run: |
-          ./gradlew clean assembleDebug testDebugUnitTest --no-daemon
+          ./gradlew clean assembleDefaultDebug testDefaultDebugUnitTest --no-daemon
           apks=$(find app/build/outputs \( -name '*.apk' -or -name '*.aab' \) -print0 | tr '\0' ',' | sed 's/,$//')
           echo "apks=$apks" >> "$GITHUB_OUTPUT"
-
-  test-patch:
-    runs-on: ubuntu-latest
-    needs: pre-commit
-    steps:
-      - name: Checkout the code
-        uses: actions/checkout@v6
-        with:
-          fetch-depth: 1
-      - name: Test applying patch
-        run: |
-          git apply app/src/patches/play_store.patch
-          git diff